This invention relates generally to cannulas adapted for both mouth and nasal use to monitor breathing, in particular, a method of manufacturing a cannula adapted to interconnect with both nasal passages and the mouth for use to monitor breathing, especially for the detection of apnea.
Nasal cannulas are commonly used to administer gases, such as oxygen, to humans having respiratory problems. Illustrations of nasal cannulas used for this purpose are found in U.S. Pat. No. 3,802,431. Nasal cannulas have been used also for inhalation therapy, made possible by development of inhalation sensors such as described in U.S. Pat. No. 4,745,925. A nasal cannula can be used to monitor breathing and for detection of apnea (the absence of breathing) when connected to an inhalation sensor.
Nasal cannulas additionally adapted to communicate with the mouth of humans to permit administration of fluids or sensing of apnea during periods of mouth breathing or nasal blockage are also known.
The present invention is a novel method of manufacturing a cannula to communicate with both nasal and oral passages. This method provides in the preferred embodiment, disconnectable mandrels, which when assembled form a mold over which a cannula forming polymeric material is applied, and which, through the capability of being disconnected, each mandrel part from the other(s), facilitates removal of the mandrels from the formed cannula.
The prior art of dipping a part in a plastisol to create a coating thereof is exemplified by U.S. Pat. Nos. 3,906,071, 4,695,241 and 4,800,116, the disclosures of which are hereby incorporated by reference.
It is an object of the invention to provide a method of manufacturing cannulas using an assembly of disconnectable mandrels over which cannula forming polymeric material is applied. Application of the plastics material over the mandrel assembly and subsequent extraction of the mandrel sections following curing of the cannula material provides a finished cannula with contiguous internal flow paths to monitor a patent""s breathing.
It is a further object of the invention to provide a multi-part mandrel assembly for forming a cannula which facilitates extraction of the mandrel assembly sections after at least partial curing the polymeric material forming the cannula.
Still another object of the invention is to form the main body forming mandrel as two separate, slightly spaced apart components which remain spaced apart from one another by a void, during the dipping process, so that the void becomes filled with a plastisol to form a septum or barrier which divides the internal passage into two compartments or passageways, one which facilitates the supply of supplemental oxygen to a patient while the other facilitates monitoring of the breathing of the patient.
According to the invention, there is provided a method of forming a cannula comprising separable parts including the steps of providing a cannula mandrel assembly, said assembly comprising at least one nare forming mandrel, at least one mouthpiece forming mandrel, and a main body forming mandrel; heating the cannula mandrel assembly to a desired temperature; providing an uncured cannula forming polymeric material in flowable state; applying at least one coating of the material to the cannula mandrel assembly to provide a desired coating material thickness on the cannula mandrel assembly to form the cannula; at least partially curing the material coating the cannula mandrel assembly; and disassembling the cannula mandrel assembly and withdrawing the at least one nare forming mandrel, and the at least one mouthpiece forming mandrel and the main body forming mandrel from the cannula.
Also according to the invention there is provided a method of forming a cannula comprising the steps of providing cannula mandrel assembly parts, said parts comprising a pair of nare forming mandrels, a main body forming mandrel having a central rectangular recessed section and openings to receive and engage ends of the nare forming mandrels, and a mouthpiece forming mandrel having an end connector, the end connector defining a slot dimensioned to mate slidingly with the rectangular recessed section; assembling the parts to provide a cannula mandrel assembly defining interior spaces of the cannula; heating the cannula mandrel assembly to a desired temperature; providing a cannula forming polymeric material as a plastisol; dipping the heated cannula mandrel assembly in the plastisol to provide a desired thickness of partially cured polymer on the cannula mandrel assembly to form the cannula; heating the cannula material of the cannula to further cure the cannula material; and extracting the nare forming mandrels, the mouthpiece forming mandrel by removing the slot from the rectangular recess, and the main body forming mandrel from the cannula.
Also according to the invention there is provided a method of forming a cannula comprising the steps of a) providing parts for a cannula mandrel assembly comprising a nare forming mandrel, a main body forming mandrel and a mouthpiece forming mandrel having an end connector to slidably engage the main body forming mandrel; b) removably mounting the nare forming mandrel to the main body forming mandrel to provide a desired orientation of the nare forming mandrel relative to the main body forming mandrel and slidably engaging the connector with the main body forming mandrel to provide a desired orientation of the mouthpiece forming mandrel relative to the nare forming mandrel and the main body forming mandrel to form the cannula mandrel assembly; c) heating the cannula mandrel assembly to a desired temperature; d) dipping the heated cannula mandrel assembly into a plastisol of a polymeric material to provide a desired thickness of polymeric material on the cannula mandrel assembly to form the cannula; e) at least partially curing the polymeric material; f) extracting the nare forming mandrel, the mouthpiece forming mandrel, and the main body forming mandrel from the cannula by reversing the assembly steps of subparagraph b).
Also according to the invention there is provided a cannula mandrel assembly, defining the interior cavity of a cannula having a main body, a nare and a mouthpiece, comprising an elongate nare forming mandrel; an elongate mouthpiece forming mandrel; and an elongate main body forming mandrel defining a recessed rectangular section slidably receiving, engaging and supporting a connector end feature of the mouthpiece forming mandrel and defining a transverse opening receiving, engaging and supporting an end of the nare forming mandrel.